The present invention relates to solid-state amplifier circuits, and particularly concerns a summing-amplifier design tolerating large common-mode voltages on its inputs.
Frequently, two differential voltage signals must be summed in an environment where they may be separated by a large common-mode voltage. One representative application for such a circuit is in a voice-coil driver for a servo system of a magnetic disk drive.
Previous circuits for performing such a function employ precision resistor networks and additional amplifiers for isolating the input signals from each other, matching impedances, and proper scaling. Such circuits are expensive, complex, or inaccurate.